When declaring a panel, what does the 'bl_context' value need to be?
In you specific case, the bl_context you are looking for is sculpt_mode. There are many others including:


objectmode
mesh_edit
curve_edit
surface_edit
text_edit
armature_edit
mball_edit
lattice_edit
pose_mode
imagepaint
weightpaint
vertexpaint
particlemode